He is a rescue and we have had him about a month now, I don't know what's going on and we really need help.

He didn't have this problem when we got him but constantly laid on his back and scratched his butt on the carpet (we thought it was cute) and now he's attacking his tail and right above his tail to the point he can't sit still and he starts shaking.

We have tried medicated shampoos and recently bought a open wound spray since he can't leave it alone.

RECENT UPDATE: at 4:36 this morning he had diarrhea (which never happens, he never poops in the house nor have we even seen him poop period, we always thought he was private about it) he ran to our room and seemed upset that he would be in trouble or telling us he needed to go out... I took him out and as soon as we hit the grass in the lawn he tried pooping but yelped and then ran away back to the porch.

It could be stress related or an allergy - with the latter - you might need to talk to a vet. Also might be worth considering putting an e collar on him till it heals. Some dogs do end up a bit neurotic due to abuse - but that's outside my experience.
– Journeyman GeekSep 28 '17 at 6:40

Yes when we got him he had a rash or bald line all around his neck from a collar. We weren't sure if him rolling around like he does caused it or if they had it on him too tight and never loosened it.
– Heather HaleSep 28 '17 at 6:43

Also looks alot like a hot spot. This could also be an allergy/allergic reaction to weed, or grass exposed to with change of environment (grass very common in small dogs). Shaking can be a part of the reaction as well, due to the itch and irritation. This is also common in flea dermititis, allergic reaction to fleas, flea bites and or mites.
– Christy B.Sep 28 '17 at 16:19

If it pains him to move his back end, he may be trying to avoid going #2, thus causing upset stomach. And the yelping could've been from the discomfort of his poo he held in, or from the movement of his backside. Holding it in to avoid pain would also be a cause of last minute panic, and pooping on floor when he can't hold it anymore. Is he on flea prevention? Were you ever told he had allergies? When was he last seen by a vet? Thanks
– Christy B.Sep 28 '17 at 16:24

We took him to the vet and he had worms and he couldn't reach them. They shaved and cleaned the area, gave us Ned's and a cone.
– Heather HaleSep 28 '17 at 23:12

1 Answer
1

Skin problems need to be seen by a veterinarian, anything you read online will be speculative and not concrete as test may need to be ran (i.e skin scraping or biopsies), medications need to be prescribed and an exam of the area in question needs to be in person (check for infection).

It could be a number of things:

Allergies

Injury that is not healing from constant chewing

Back injury (spine) that is causing discomfort and making him chew (you mentioned difficulties hunching to excrete his bowels)